1. Field of the Invention
This invention relates to sampling method and apparatus for analytical equipment and, in particular, to such method and apparatus that is adapted for automatically performimg series analyses.
2. Description of the Prior Art
In U.S. patent application Ser. No. 660,194 filed on Feb. 20, 1976 and assigned to the Assignee of the present application, there is disclosed apparatus wherein samples to be measured are taken up from successive sample containers and sequentially supplied to an atomic absorption spectrometer. Means are provided to prevent errors in the measured results due to carry-over of the sample material or other contaminations. The automatically controlled sequence of the individual operating steps permits series analyses to be performed, whereby the measured signals may be evaluated in a data processor.
It will be appreciated that such a method of analysis, however, will not always yield reliable measuring results, particularly if the signals obtained depend on detector sensitivity or sample composition. Thus, for instance, the indicator sensitivity of thermionic detectors in gas chromatography which respond selectively to halogen, phosphorus or nitrogen containing compounds are dependent on ageing effects. In sample liquids like blood, substances which are inherently present may affect the signal measured so that a calibration curve obtained for one liquid sample may not be applicable to the same sample of different origin. In such cases it is, therefore, necessary to conduct separate reference measurements for each individual sample.
In methods of measurement responsive to the quantity of the component to be determined in the sample, i.e., gas chromatography and atomic absorption spectroscopy, the procedure is to perform at least one additional measurement with the same sample, with a known amount of the component to be determined being added to the sample. Said known amount is added as a metered quantity of a liquid additive containing the desired component dissolved in a solvent. Additionally, a corresponding quantity of the pure solvent is added to the sample being measured, per se, before taking its measurement. The respective dilution is then taken into consideration in the subsequent evaluation of the measured signals. See, for example, the publication entitled, "Analysentechnische Berichte", Vol. 32, (1974) page 10.